Yarn brakes for two-for-one twisting spindles have been known for a long time in various configurations and are described, sometimes in detail, in numerous patents. Yarn brakes of this type are, in particular, used in two-for-one twisting processes and ensure that the yarn receives a specific pretensioning during the twisting process.
A two-for-one twisting spindle with a yarn brake, which is configured as a brake cartridge, is known, for example, from DE 31 39 236 C2. In yarn brakes of this type configured as brake cartridges, two cylinders pressed apart from one another by a spring element and slidable telescopically relative to one another are supported by their spherical ends on brake faces, which are arranged in the region of a yarn inlet opening or a yarn outlet opening of a brake housing and, in the process, clamp the yarn that is traveling through the brake housing.
The drawback in brake cartridges of this type is, however, that the pretensioning of the yarn during the twisting process is only predetermined by the spring force of the spring element of the brake cartridge and, at least during the twisting process, cannot be corrected. Furthermore, brake devices for two-for-one twisting spindles are known, for example, from German Patent Publication DE 33 36 715 C2 or U.S. Pat. No. 7,000,865 B1, which in each case have a ball which rests in a brake housing on a brake face. In this type of brake device, the braking force acting on the yarn that is traveling through the brake housing is dependent on the ball's own weight; in other words, the pretensioning of the yarn can be adjusted up to a certain extent by the diameter of the ball. In brake devices configured in this manner, the achievable braking force is relatively low in each case, however. In order to be able to realize higher pretensionings, it has therefore already been proposed that a plurality of ball brakes of this type be arranged one behind the other. German Patent Publication DE 197 55 825 A1 describes a two-for-one twisting spindle for twisting natural silk, the yarn brake of which has a total of seven brake ball devices arranged one behind the other. Brake devices of this type not only require a relatively large installation space, but are extremely disadvantageous with regard to threading a new yarn.
Yarn brakes for two-for-one twisting spindles are also known from German Patent Publication DE-GM 81 10 891, in which an upper piston, which is loaded by a spring element and is equipped with a first upper brake face, acts on a brake ball, which is thereby in turn pressed onto a second, lower brake face. By rotating a spring element abutment, the pretensioning of the spring element and therefore the contact pressure of the brake ball on the brake faces can thus be adjusted in a defined manner. In this known yarn brake, the brake ball can also be raised pneumatically, which considerably facilitates the threading of a new yarn into the yarn brake.
The drawback in this type of yarn brake is, however, that the spring-loaded piston, which has the upper brake face, slides virtually without play in an axial guide of the yarn brake housing. In other words, the upper brake face cannot move away laterally, which leads to the fact that yarn anomalies such as knots, thick locations, lumps of dust, etc., lead to strong yarn tension increases through to yarn breaks.